Magnetoresistive sensors, which utilize the magnetoresistive effect in which electrical resistance changes in response to changes of the external magnetic field, is known as a good magnetic field sensor and is used practically as a read head in magnetic heads, a key component of magnetic storage devices.
With the progress in size reduction of magnetic recording and reproducing devices, improvements in the performance of magnetic heads to read and write information would enable the heads to operate even better. Currently, a magnetic head generally has two heads: a read head to read information, and a write head to write information. Commonly, the read head is a CPP structure magnetoresistive effect head enabling high read resolution.
To realize still higher recording densities, some problems associated with the read head may be solved. The problems include higher accuracy fabrication of the read head element section and improvement in the stability of the read performances.
Raising the recording density involves narrowing the read track width. Here, the read track width is the across-the-track width of the magnetoresistive sensor film which detects a signal from a recording medium. Preferably, in view of productivity, the read track width is formed during the lift-off process, since it is a simple process. For this purpose, the height of the lift-off mask material has a certain level. To form a narrow read track width, the pattern width of the lift-off mask material is narrowed. Therefore, the ratio of the height to the pattern width in the lift-off mask material (aspect ratio) becomes high, which may result in a lowered pattern accuracy of the lift-mask material due to bending, collapse of the mask pattern, etc. In addition, the stripe height has an effect on the performance of the read head, and may also be formed with a higher accuracy. The stripe height is the length of the magnetoresistive sensor film in the depth direction.
Narrowing the read track width affects the stability of the read performances, too. Generally, to stably reproduce a good waveform with sufficiently low noise, the stripe height is shortened, which corresponds to a narrow read track width. This is because the magnetic anisotropy is one of the factors affecting the stable operation. The magnetic anisotropy is determined by the shape of the free layer in which magnetization rotates depending on the magnetic field from the recording medium. The free layer is one of the ferromagnetic layers which comprise the magnetoresistive sensor film.
In addition, the free layer is provided with a longitudinal bias layer on each side thereof, via an insulator layer in a track width direction, to apply a longitudinal bias field thereto so that the magnetization rotates without causing noise. Shortening the stripe height makes the longitudinal biasing layer more subject to thermal fluctuations since the length of the longitudinal biasing layer in the stripe height direction inevitably becomes shorter.
Japanese Patent Office (JPO) Pub. No. JP-A-2005-346869 and JP-A-2008-84373 disclose CPP structure magnetoresistive heads each comprising a magnetoresistive sensor film and longitudinal biasing layer whose stripe height is longer than that of the magnetoresistive sensor film.
Each of these current structures has problems associated with their use and/or production. Therefore, a magnetoresistive sensor which eliminates or lessens these problems would be beneficial to the field of magnetic recording.